Conditional step/stage in Jenkins pipeline

Question

How do you run a build step/stage only if building a specific branch?

For example, run a deployment step only if the branch is called deployment, leavin

Answer 1

Doing the same in declarative pipeline syntax, below are few examples:

stage('master-branch-stuff'){
  agent any
  when{
    branch 'master'
  }
  steps {
    echo 'run this stage - ony if the branch = master branch'
  }
}

stage('feature-branch-stuff') {
    agent label:'test-node'
    when { branch "feature/*" }
    steps {
        echo 'run this stage - only if the branch name started with feature/'
    }
}

stage('expression-branch') {
    agent label:'some-node'
    when {
    expression {
        return env.BRANCH_NAME != 'master';
        }
    }
    steps {
        echo 'run this stage - when branch is not equal to master'
    }
}

stage('env-specific-stuff') {
    agent label:'test-node'
    when { 
      environment name: 'NAME', value: 'this' 
    }
    steps {
        echo 'run this stage - only if the env name and value matches'
    }
}

More effective ways coming up - https://issues.jenkins-ci.org/browse/JENKINS-41187
Also look at - https://jenkins.io/doc/book/pipeline/syntax/#when

---

The directive beforeAgent true can be set to avoid spinning up an agent to run the conditional, if the conditional doesn't require git state to decide whether to run:

when { beforeAgent true; expression { return isStageConfigured(config) } }

Release post and docs

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UPDATE
New WHEN Clause
REF: https://jenkins.io/blog/2018/04/09/whats-in-declarative

equals - Compares two values - strings, variables, numbers, booleans - and returns true if they’re equal. I’m honestly not sure how we missed adding this earlier! You can do "not equals" comparisons using the not { equals ... } combination too.

changeRequest - In its simplest form, this will return true if this Pipeline is building a change request, such as a GitHub pull request. You can also do more detailed checks against the change request, allowing you to ask "is this a change request against the master branch?" and much more.

buildingTag - A simple condition that just checks if the Pipeline is running against a tag in SCM, rather than a branch or a specific commit reference.

tag - A more detailed equivalent of buildingTag, allowing you to check against the tag name itself.